The present invention relates to the field of the use of cable in constructions.
It finds an application each time it is necessary to retain a construction element with respect to a structural cable, or alternatively to retain the structural cable with respect to the construction element, so as to avoid relative movements thereof parallel to the direction of the cable.
The term xe2x80x9cstructural cablexe2x80x9d as used here also covers a bundle or group of individual cables roughly parallel to one another, it being possible for each individual cable itself to be made up of one or more elemental wires. The cable or the individual cables may be bare or individually sheathed, or alternatively may consist of a mixture of these two types. The cable may possibly be contained in an overall external protective sheath filled with an adhesive material. In the case of a cable formed by a group of individual cables, these may be in direct contact with one another or may be spaced apart.
The invention can be implemented in particular in suspension bridges comprising one or more suspension cables which have to be immobilized with respect to certain elements (the tops of towers, etc), and to which certain other elements (deck hangers, sections integral with the deck, etc) need to be attached.
The invention can also be applied to the field of prestressing, the structural cable then consisting in a cable that is tensioned in order to exert prestressing forces on a construction made of concrete or some other material, and to which certain elements of the construction can be fixed.
In the fixing area, the interface that the cable exhibits to its environment is generally defined by generators which are essentially parallel to the longitudinal direction. Under these conditions, in order to prevent relative longitudinal movements between the cable and the element, a transverse clamping force has to be exerted on the cable in order to obtain sufficient friction at the interface.
This clamping can be obtained using wedge-effect jaws, particularly to anchor structural cables. In the common case of a multi-strand cable, the jaws are installed individually around the strands, which entails that these can be parted from one another, a condition which is not always fulfilled in practice.
Otherwise, clamping is habitually exerted using collars comprising two (or more) shells, urged toward one another by means of bolts or the like. The inside of the shells has a shape corresponding to the external interface of the cable, possibly supplemented by filler inserts.
This approach leads to a non-uniform transmission of clamping forces across the section of the structural cable, even though it is possible to combat this disadvantage by appropriate filling of the inside of the collar (see EP A-0 789 110). Around the periphery of the cable, the areas next to the gaps that separate the shells tend to be less heavily loaded than the others. What this means is that in order to obtain a nominal clamping value, excessive clamping needs to be applied, this being undesirable as far as the reliability of the device and the integrity of the cable are concerned. Along the cable, the collar transmits maximum force in the region of the bolts, of which there have therefore have to be many if the collar is relatively long. Furthermore, applying transverse clamping stresses to the shells entails these having an accordingly robust structure and thickness, which makes the fixing device relatively heavy.
German patent 869 977 proposes securing the fixing of a hanger to the suspension cable of a suspension bridge by adding wedge-effect jaws to the two ends of a collar consisting of several shells clamped together by bolts. This securing function is rather relative because the wedge effect is largely lost if the bolts that clamp the shells together lose their tightness as a result of creep or fatigue. Furthermore, the distribution of the clamping forces is not well controlled if these bolts are retightened. In addition, this device presents the bulk and weight problems customarily posed by this type of collar.
Another disadvantage of the collar in German patent 869 977 is that clamping is achieved by moving the jaws toward one another parallel to the cable. This results in significant friction at the surface of the cable, this being all the more exacerbated since the interior face of the jaws has to be rough in order to grip the cable firmly. This is already problematical in itself with bare metal wires and is clearly unacceptable when the cable or its constituent wires are coated with a plastic sheath.
One object of the present invention is to propose a fixing method which suitably distributes the forces transmitted to the structural cable.
The invention therefore proposes a device for fixing together a construction element and a structural cable, comprising a rigid housing connected to the construction element and consisting of a one-piece part which completely surrounds a portion of the cable, a wedging structure arranged between the cable and housing, and load transmitting means designed to exert a longitudinal compressive force parallel to the cable, on the wedging structure, the wedging structure being pressed against the cable and the housing under the action of the longitudinal compressive force, so as to offer resistance to the movement of the housing and of the construction element parallel to the cable.
The cable is gripped by the friction that results from the orthogonal contact pressures generated by the longitudinal compression of the structure contained between the rigid outer housing and the cable passing through it.
The load transmitting means make it possible to control the integrity of the fixing and the precise positioning of the housing with respect to the cable. Minimum compressive force can be applied before the device is definitively mounted, or during this mounting prior to the application of load.
The wedging structure must naturally have sufficient compressive strength and shear strength. Its longitudinal displacement when the compression is applied results in uniform radial clamping of the cable.
This wedging structure may be made up of rigid elements such as frustoconical keys, which generate the clamping force as the axial compression is applied, because of the reaction exerted by the frustoconical orifice of the housing in which they are engaged. As a preference, just one end of the housing has a frustoconical orifice receiving a frustoconical jaw urged toward the opposite end of the housing. Thus, when force is applied, the jaw does not rub against the cable. It is rather the housing which moves toward the largest-section end of the jaw in order to press it against the cable without damaging the latter.
Uniform transmission of the forces at the interface between the wedging structure and the cable can be made even easier when the wedging structure undergoes a certain amount of deformation at the time when the load transmitting means exert the controlled longitudinal compression.
This deformation may consist in limited creep of the material of which the wedging structure is formed, which may in particular have the shape of a frustoconical jaw. The limited creep may also occur at the housing or at an insert arranged around a rigid frustoconical jaw.
According to another possibility, the deformation is due to the intrinsically deformable nature of all or part of the wedging structure housed between the housing and the cable. This structure may then comprise an elastic material, a granular material, a fibrous material or alternatively a mixture of such materials, and may be made in one or more pieces. It has the property of expanding in the direction or directions orthogonal to the direction or directions of compression, either through intrinsic elastic movement or through the movement of the individual particles (fibrous and/or granular) with respect to each other or with respect to a binder. The deformable structure has a fairly high shear strength when compressed between the housing and the cable, so as to oppose relative longitudinal movement of these items.
The housing acts as a thrust face for the wedging structure and for the piece for connecting with the element to be fixed to the cable. It is a one-piece part, for example cylindrical on a circular or polygonal base, which completely surrounds a portion of the cable. This housing may be made of a metal or any other sufficiently rigid material. It has the advantage of being able to be of a relatively lightweight construction.
The longitudinal compression is transmitted to the wedging structure by means of plates or rings or other parts bearing on the end surfaces of the wedging structure. The compression may be applied at one end, the other bearing against a stop integral with the housing, or to both ends of the wedging structure, over all or just part of the accessible surface.
The load transmitting means may comprise one or more members running parallel to the cable, tensioned by tightening means so as to exert the longitudinal compressive force to the ends of the wedging structure. These tension members (bolts, prestressing strands or any other appropriate member) may pass through the wedging structure or alternatively around it, through or around the outside of the housing. The load transmitting means may also comprise a nut screwed into a screw thread integral with the housing and applied against one end of the wedging structure.
In another embodiment proposed here, a device for fixing together a construction element and a structural cable, comprises a rigid housing connected to the construction element and surrounding the cable, a wedging structure comprising at least one deformable material, and arranged between the cable and housing, and load transmitting means designed to exert a longitudinal compressive force parallel to the cable, on the wedging structure, the wedging structure being pressed against the cable and the housing under the action of the longitudinal compressive force, so as to offer resistance to the movement of the housing and of the construction element parallel to the cable. In this last embodiment, the housing is not necessarily of one piece, although this is preferred. The load transmitting means may be in accordance with those already mentioned. As an alternative, they may be arranged to convert a longitudinal component of the load exerted on the cable by the construction element into a longitudinal compression of the deformable structure.
Other aspects of the invention relate to a method, using a device of the aforementioned type to fix a construction element to a structural cable or, symmetrically, to fix a structural cable to a construction element, and to a suspension bridge.